The present invention relates generally to communication systems, and more specifically to multi-channel filtering systems and transceiver architectures having variable transmission and reception bandwidths.
Present day communication systems are often limited in their reliability and speed by adjacent channel interference. Adjacent channel interference, or “spectral crowding” as it is referred to in wireless communication systems, occurs when one or more received signals occur adjacent to the intended signal, the adjacent signal's proximity and/or signal strength relative to the intended signal being such that the destination receiver is critically limited or unable to process the intended signal accurately. The problem often results in poor quality or dropped connections when a large number of users attempt to use the particular system's available bandwidth, as each user provides a potentially interfering signal to the other's intended signal. In addition, the interference tends to be intermittent; for example, the communication system may be more heavily used during one period of time as opposed to others, or the source of the interference itself may be temporary, e.g., a mobile telephone user who is allocated to an adjacent channel in an otherwise uncrowded spectrum.
FIG. 1 illustrates a conventional transceiver 100 used in establishing a wireless communication network link in which the transmitter and receiver functions are not operated concurrently. The conventional transceiver 100 consists of a transceiver front-end 120, a filter 134 connected between two 2-pole, single throw switches 132 and 136, and a transceiver back-end 140. Each of the 2-pole, single throw switches have a receive pole and a transmit pole. During a receive operation, both switches connect to their receive poles, thereby completing the receive channel through filter 134. Similarly during signal transmission, both switches connect to their transmit poles to complete the transmit channel through the filter 134. Using this transceiver topology, filter 134 may be used in both transmit and receive modes of operation.
The conventional transceiver 100 does not provide a solution to the adjacent channel interference problem, as it employs a single filter 134 which may be too wide in some circumstances, and too narrow in others. For example, when the conventional transceiver 100 is operated in an environment or during a time when there are many adjacent channel users, the filter 136 may be too wide, and not provide the requisite amount of adjacent channel rejection during reception. During other times when adjacent bands are relatively free, the filter 136 may be too narrow, limiting the communication rate unnecessarily.
What is needed is an improved transceiver architecture which is adaptable to limit the transceiver's bandwidth when adjacent signal interference is present, and to widen the transceiver's bandwidth to increase the communication rate when conditions permit.